A video encoder compresses video information so that more information can be sent over a given bandwidth. The compressed signal may then be transmitted to a receiver that decodes or decompresses the signal prior to display.
High Efficient Video Coding (HEVC) is a new video compression standard planned to be finalized by the end 2012. It is currently under development by the Joint Collaborative Team on Video Coding (JCT-VC) formed by ISO/IEC Moving Picture Experts Group (MPEG) and ITU-T Video Coding Experts Group (VCEG). The team will also standardize a Scalable Video Coding (SVC) extension of HEVC standard.
In the current HEVC specification, a picture is coded in the unit of Largest Coding Unit (LCU). A LCU can be a 128×128 block, a 64×64 block, a 32×32 block or a 16×16 block. A LCU can be encoded directly or be divided into 4 Coding Unit (CU) for next level encoding. For a CU in one level, it can be encoded directly or be further divided into next level for encoding. The smallest CU is 8×8.
In general, at each level a CU whose size is 2N×2N, may be divided into different size of Prediction Units (PU) for prediction. For intra coding, a 2N×2N CU can be encoded in one 2N×2N PU or in four N×N PUs. For inter coding, a 2N×2N CU can be encoded in one 2N×2N PU, or two 2N×N PUs, or two N×2N PUs, or 0.5N×2N PU+1.5N×2N PU, or 1.5N×2N PU+0.5N×2N PU, or 2N×0.5N PU+2N×1.5N PU, or 2N×1.5N PU+2N×0.5N PU, or four N×N PUs.
In non-gray pictures, a picture consists of the data of three channels, i.e., Luma channel Y and two Chroma channel U and V. And correspondingly, a PU consists of one luma block Y and two Chroma blocks U and V.
In an HEVC encoder, after intra prediction (Intra-frame Prediction module) or inter prediction (Motion Estimation and Motion Compensation modules) are performed, the prediction samples corresponding to the difference between an input PU and the predicted PU are transformed and quantized for entropy coding. When a PU is encoded in intra coding mode, different intra prediction modes may be applied including DC prediction, planar prediction, horizontal prediction, vertical prediction and so forth.
As the standardization of the main part of HEVC is reaching completion, JCT-VC has started planning to add a Scalable Video Coding (SVC) extension into HEVC standard. SVC is an important issue to cope with the heterogeneity of networks and devices in modern video service environment. A SVC bit stream contains several subset bit streams that can themselves be decoded, and these sub streams represent the source video content with different resolution, frame rate, quality, bit depth, and etc. The scalabilities are achieved by using a multi-layer coding structure. In general, there's one Base Layer and several Enhancement Layers in a SVC system.